Raman spectroscopy is similar to infrared (IR), including near infrared (NIR), spectroscopy but has several advantages. The Raman effect is highly sensitive to slight differences in chemical composition and crystallographic structure. This characteristic makes it very useful for the investigation of illegal drugs as it enables distinguishing between legal and illicit compounds, even when the compounds have similar elemental compositions. Also, when using IR spectroscopy on aqueous samples, a large proportion of the vibrational spectrum can be masked by the intense water signal. In contrast, with Raman spectroscopy, aqueous samples can be more readily analyzed since the Raman signature from water is relatively weak. And, because of the poor water signature, Raman spectroscopy is often useful when analyzing biological and inorganic systems, and in studies dealing with water pollution problems.
Raman scattering may be regarded as an inelastic collision of an incident photon with a molecule. The photon may be scattered elastically, that is without any change in its wavelength, and this is known as Rayleigh scattering. Conversely the photon may be scattered inelastically resulting in the Raman effect.
Taggant technology is most commonly used for detection and source identification. In one common detection application, chemical or physical markers are added to explosives during their manufacture. Then, detection of this taggant can then be used to indicate the presence of the explosive during airport screening, for example. In an identification application, the taggants are engineered to survive the explosion so that they can be used to identify the source of the explosives as part of a forensic operation in which a unique Raman spectra for taggants are associated with the batch of explosives containing the taggants.
Taggant technology is being proposed for many new commercial applications. It can be used to manage supply chains for articles to ensure that the articles originated from the specified source and are not counterfeit or gray-market. Markets include aircraft parts, stamps, negotiable financial instruments (such as currency, checks, stamps, vouchers, stock certificates, bonds, script, food stamps), identification and travel documents (such as passports, ID cards, visas, health cards,), identification labels (apparel industry), packaging or seals on items such as CDs, DVDs and software. Of particular concern is counterfeiting in the pharmaceutical industry. This has raised special concerns from the healthcare and pharmaceutical industries, as well as Food and Drug Administration (FDA) regulators. Instead of simple economic loss, manufacturers' and distributors' reputations, counterfeit drugs put patient lives at risk.
A number of taggant technologies exist, such an NIR and fluorescence taggants. One of the most promising taggant technologies for counterfeit prevention applications are Raman taggants. These are typically organic, monomeric or polymeric compositions that have Raman active components, such as azo, azomethine or polycyclic chromophores, polydiacetylenes colloids or other nano scale metal particles, or phtalocyanines. Information is encoded by the taggants relating or associating the unique Raman spectra of the taggants to information about a given article. The taggants' information is obtained by irradiating the taggants with light, such as from a laser, and then detecting the spectral response in the Raman wavelengths. The detected spectrum is then matched against spectra in library to identify the taggants and thereby derive the information about the article associated with the identify taggants.